The field of this invention is that of fuel supply systems for internal combustion engines and the invention relates more particularly to a fuel supply system having an electric choke in which a heater is arranged to heat a thermally responsive coil spring to regulate choke operation and wherein novel and advantageous control means energize and deenergize the heater in particular sequence in a novel and advantageous manner to achieve improved choke operation.
Conventional fuel supply systems for automotive engines include a carburetor having an air-fuel induction passage for providing a mixture of air and fuel to the engine and incorporate an unbalanced-mounted, air-movable choke valve which is mounted for movement across the passage to regulate air-flow into the passage. A thermally responsive thermostat metal coil spring is operatively connected to the choke valve and is movable in response to increase in temperature to bias the choke valve toward a position which restricts air flow into the passage with a force which decreases over a selected force range in response to increase in temperature of the coil spring over a selected temperature range. The coil spring is heated in response to increase in engine or engine coolant temperature or in response to operation of electric heating means or the like to regulate choke operation to facilitate engine starting and engine warm up on a cold day.
In some conventional systems as shown in U.S. Pat. No. 4,083,336 for example, a heater is arranged so it is usually operated on a warm day when very little choking operation is required. On a cold day, the heater is not normally energized when engine operation is initiated but is usually energized only after a period of engine warm up has occurred when thermally responsive switch means located near the heater have been heated to a selected temperature. In that arrangement, operation of the heater on a cold day primarily serves to bring about a more rapid final opening of the choke. In some applications of systems, the choke valve may start to open more slowly than is desirable so there is an initial period of operation after engine starting when the system achieves poorer fuel economy than is necessary for achieving smooth engine start up. On the other hand, if the thermostat metal coil were modified to start to open the choke valve more quickly to improve fuel economy, the choke valve would tend to open too far before adequate engine warm up occurs and would tend to cause poor engine driveability during a part of the engine warm up period, particularly where sharp engine acceleration occurs during the warm up. In other known systems such as that shown in U.S. Pat. Nos. 3,806,854 and 4,237,077 for example, one heater is energized on initiation of engine operation on a cold day and a second heater is activated to supplement that heating after a degree of engine warm up occurs. In those systems, the choke valve also starts to open relatively slowly and then opens at a faster rate after some engine warm up has taken place. In one known fuel supply system as shown in U.S. Pat. No. 4,331,615, the system provides relatively rapid reduction in choke valve biasing force when the choke valve first starts to open and then provides relatively slower opening of the choke to maintain adequate engine driveability during the main part of the engine warm up period. However that fuel supply system is relatively more complex than is desired for many high volume applications and it would be desirable if that particular form of choke operation could be achieved in a more compact and economical way.